The goal of this research project is to understand the nature of mouse embryonic and adult stem cells and to identify genes that are responsible for the maintenance of cellular pluripotency. We have been conducting global gene expression profiling with the mouse embryonic DNA microarrays developed in our laboratory. We have now completed the expression profiling of mouse embryonic stem (ES) cells, trophoblast stem (TS) cells, adult neural stem (NS) cells, ES cells undergoing neural differentiation in culture, F9 embryonal carcinoma (EC) cells undergoing endoderm differentiation, and ES cells undergoing trophoblast differentiation. We are currently analyzing these data by Principal Component Analysis (PCA) and other statistical and bioinformatic analyses. We have also completed the microarray analysis of ES cells, in which the level of Oct3/4 - a gene critical for maintenance of undifferentiated ES cells - is controlled by tetracycline-inducible system, and have identified a number of downstream target genes of Oct3/4. These studies begin to provide the gene regulatory pathways involved in the maintenance and differentiation of stem cells.